Apparatus for measuring magnetic particles suspended in a fluid based on fluctuations in an induced voltage

Abstract

An apparatus for detecting magnetic particles suspended in a liquid, such as particles suspended in lubricating oil flowing through an engine. The oil is caused to pass through the area coupling two or more coils while the mutual inductance of the coils is monitored. When a magnetic particle enters the area coupling the coils, the mutual inductance of the coils will increase, thereby indicating the presence of the particle.

We claim: 
     
       1. A method for predicting the failure of a lubricated machine by detecting magnetic particles suspended in a liquid used to lubricate the machine, said method comprising the steps of: energizing a first coil with an electrical signal to induce a voltage in a second coil coupled to said first coil;   passing said liquid through the region coupling said coils;   processing said voltage induced in said second coil to detect fluctuations in said voltage; and   indicating the presence of magnetic particles in said liquid in response to said detected fluctuations to thereby predict whether said machine will fail.   
     
     
       2. The method of claim 1 wherein said machine is an engine. 
     
     
       3. The method of claim 1 wherein said step of processing further comprises processing said electrical signal. 
     
     
       4. The method of claim 1 wherein said step of passing comprises passing said liquid through a conduit. 
     
     
       5. The method of claim 4 wherein said coils are wound around said conduit, such that said liquid passes through each of said coils. 
     
     
       6. The method of claim 1 further comprising the step of energizing a third coil with an electrical signal, said third coil coupled to said second coil to thereby induce a second voltage in said second coil, wherein said step of passing further comprises passing said liquid through the region coupling said second coil and said third coil and wherein said step of processing further comprises processing said second voltage. 
     
     
       7. The method of claim 6 wherein said first coil and said third coil are connected together in series. 
     
     
       8. The method of claim 6 wherein said voltage induced in said second coil by said first coil is out of phase with said voltage induced in said second coil by said third coil. 
     
     
       9. The method of claim 8 wherein said step of indicating comprises indicating the presence of a magnetic particle if two of said fluctuations are detected, and if said two fluctuations are out of phase. 
     
     
       10. The method of claim 6 wherein said step of passing comprises passing said liquid through a conduit. 
     
     
       11. The method of claim 10 wherein each of said coils is wound around said conduit such that said liquid passes through each of said coils. 
     
     
       12. The method of claim 11 wherein said first coil and said third coil are wound around said conduit in opposite directions. 
     
     
       13. The method of claim 6 wherein each of said fluctuations comprises an increase in the magnitude of said induced voltage, said increase occurring when a magnetic particle is located in either the region coupling said first and second coils or the region coupling said second and third coils. 
     
     
       14. The method of claim 13 wherein said step of indicating comprises indicating the presence of a magnetic particle if two of said fluctuations are detected. 
     
     
       15. The method of claim 1 wherein said first coil further induces a voltage in a third coil coupled to said first coil, wherein said step of passing further includes passing said liquid through the region coupling said first coil and said third coil, and wherein said step of processing further includes processing said voltage induced in said third coil. 
     
     
       16. The method of claim 15 wherein said second coil and said third coil are connected together in series. 
     
     
       17. The method of claim 15 wherein said step of passing comprises passing said liquid through a conduit. 
     
     
       18. The method of claim 17 wherein each of said coils is wound around said conduit such that said liquid passes through each of said coils. 
     
     
       19. The method of claim 18 wherein said second coil and said third coil are wound around said conduit in opposite directions. 
     
     
       20. The method of claim 15 wherein each of said fluctuations comprises an increase in the magnitude of said induced voltage, said increase occurring when a magnetic particle is located in either the region coupling said first and second coils or the region coupling said second and third coils. 
     
     
       21. The method of claim 20 wherein said step of indicating comprises indicating the presence of a magnetic particle if two of said fluctuations are detected. 
     
     
       22. The method of claim 15 wherein said voltage induced in said second coil is out of phase with said voltage induced in said third coil. 
     
     
       23. The method of claim 22 wherein said step of indicating comprises indicating the presence of a magnetic particle if two of said fluctuations are detected, and if said two fluctuations are out of phase.